This invention relates to a method of making biodegradable packaging material and packaging elements made thereby.
As is known, various techniques have been employed to manufacture loose fill packaging elements of thermoplastic materials, such as polystyrene and polyethylene materials. For example, it has been known to place a charge of a thermoplastic resin, such as polystyrene, in pellet form into an extruder at a feed point and to thereafter heat the pellets into a molten state in order to obtain a flowable molten mass. In addition, it has been known to add a blowing agent such as a hydrocarbon at a point of the extruder, for example in a mixing zone, and to mix the blowing agent into the molten mass of plastic to obtain a homogeneous flowable mass. This mass is subsequently extruded through one or more openings in a die to obtain a particular cross-sectional shape. In some cases, the extrudate is quickly cooled such as by quenching in water so that the extrudate retains a latent foaming state. The cooled extrudate is then cut into small pellets which can be subsequently packaged and shipped to a remote location where the pellets can be heated into an expanded state.
In an alternative technique, the extrudate can be allowed to expand upon extruding from the die of the extruder directly into a foamed expanded state. The foamed extrudate can then be cut into predetermined lengths to form a conventional-size packaging element.
From an ecological standpoint, loose fill packaging elements made solely of plastic materials tend to have a long life, particularly, when buried in land fills or other similar types of waste dumps. Accordingly, attempts have been made to fabricate thermoplastic elements, such as packaging materials and the like, in a fashion which permits degradability over relatively short periods of time. To this end, suggestions have been made to incorporate ingredients, such as corn starch into the thermoplastic elements in order to enhance biodegradability.
Accordingly, it is an object of the invention to reduce the costs of making biodegradable packaging material.
It is another object of the invention to provide a loose fill packaging element of unique construction which is capable of biodegrading in a relatively short time.
It is another object of the invention to provide a relatively simple technique for manufacturing biodegradable loose fill packaging elements of non-thermoplastic materials and other foam products, e.g. foam sheet, rod, plank, tubing and the like.
Briefly, the invention provides a packaging material which is made basically of a starch and which employs additives including a nucleator and a plasticizer, such as mineral oil.
The starch packaging material may be manufactured in a latent-foaming state in which the material is less bio-degradable. However, when the material is heated and expanded into an expanded state, the expanded starch is rendered more readily biodegradable when exposed to the environment. In this respect, in the latent form, there is little internal oxygen present in the starch packaging material but when expanded, each cell within the material will contain oxygen allowing a biodegradable process in conjunction with the outside environment to commence more rapidly. Biodegradability will occur more rapidly as each cell wall is surrounded by oxygen and as each cell wall becomes extremely thin during expansion. Biodegradability is particularly enhanced in the present of moisture. In this respect, the more moisture, the faster the material will decompose.
The method of making the biodegradable material, e.g. in the form of loose fill packaging elements, comprises;an initial step of mixing and heating a charge of a starch, for example, a corn starch, a nucleator and a plasticizer, if necessary to form a flowable mass. Thereafter, a blowing agent, such as an alcohol or water, is injected into and mixed with the heated flowable mass on the xe2x80x9cflyxe2x80x9d to form a homogeneous mass which is then extruded through a die to form at least one continuous extrudate. This extrudate is then cooled to limit expansion and the cooled extrudate is then cut into individual pellets having a latent-foaming characteristic. Alternatively, the extrudate can be allowed to expand (i.e. foam) after leaving the die and can then be cut into expanded elements of a size suitable for loose fill packaging or other foam items, such as, sheet, rod, plank, tubing and the like.
The pellets may be handled in the latent foaming state and shipped in a conventional manner to a user. Thereafter, the pellets can be heated in order to foam the pellets into foamed biodegradable packing elements.
The starch used to make the packaging elements is typically pure corn starch but may be any other suitable starch, such as a potato starch and the like.
The nucleator may be a mixture of citric acid and bicarbonate of soda, e.g. a mixture sold under the trademark HYDROCERAL(copyright). In the alternative, talcum powder may be used as a nucleator.
The blowing agent which is used, may for example, be an alcohol, such as glycol, or may be water. The amount of blowing agent added to the starch mass controls the amount of expansion of the mass. In this respect, the more the blowing agent, the greater the expansion up to, of course, a blow out condition in which there is an excess of blowing agent. Further, the amount of blowing agent injected can be adjusted during an extrusion process, i.e. on the fly rather than on a batch basis.
Typically, the starch which is used is a starch which contains sufficient water to bring about a flowable mass of the mixed ingredients under the heat and pressure of a conventional extruder.
The use of corn starch and the nucleator allows curing to be performed at a fast rate. Hence, the storage costs of the loose fill product can be reduced. Similarly, the product can be shipped faster. Also, the product can be put into packages and placed in stock at a faster rate.
The use of starch also renders the product biodegradable after expansion of the pellets into the foamed state. As noted above, biodegradability of the product from the latent state to the expanded state is enhanced, e.g. by a factor of about fifty after expansion. The reason for this appears to be that is little internal oxygen present in the latent form state whereas in the expanded (foamed) state, each cell will contain oxygen allowing a biodegradable process to occur in conjunction with the environment. The thinness of the cell walls also enhances the biodegradable characteristic of the expanded elements particularly since degrading occurs from the outside towards the inside of the element especially in the presence of water.